1. Field of the Invention
Noble metal thin films can be deposited by vapor deposition processes, such as atomic layer deposition. Such films find use, for example, in integrated circuits and magnetic recording media.
2. Description of the Related Art
Thin films of ruthenium and other noble metals can be used in a wide variety of applications including integrated circuits and magnetic recording media. For example, noble metals such as ruthenium and metal alloys comprising noble metals, such as RuTa, may be used as an electrode material in transistors, particularly those where silicon oxide is replaced by high-k dielectrics. Noble metals can also be used as copper seed layers in metallization processes. Noble metals are advantageous because they tend not to oxidize or otherwise corrode.
Noble metal films can also be used for capacitor electrodes of dynamic random access memories (DRAMs) and are a potential electrode material for nonvolatile ferroelectric memories.
In addition to electrode applications, thin noble metal films find potential use in magnetic recording technology. In anti-ferromagnetically coupled recording media, for example, a thin Ru film may be used for separating two ferromagnetic layers.
Ruthenium and other noble metals can be deposited by atomic layer deposition (ALD) type processes. However, the incubation time for such processes varies depending on a number of factors including the composition of the surface on which the noble metal is being deposited. In particular on metal oxides and metal nitrides, the incubation time can be long. For example, on SiO2 the incubation time can be as much as 300-400 ALD cycles. The long incubation time uses up expensive noble metal precursor and increases processing time. This can be a particular problem in the deposition of noble metal films in an ALD batch system, where 50-100 wafers are processed at the same time.
Plasma enhanced ALD (PEALD) has been shown to decrease the incubation time for depositing noble metals on a WNC surface. Unfortunately the PEALD process can not be used to deposit metal gates due to harmful effects of the direct plasma on the high-k gate oxide. Further, in the case of the deposition over structures with a high step coverage, such as inside deep and narrow capacitor containers or trenches, the life time of H radicals is too short to obtain a conformal noble metal film along the entire step.
High-k oxides can themselves be deposited using ALD prior to noble metal deposition. Generally, in the last ALD deposition cycle of a high-k oxide, such as hafnium or aluminum oxide, the outermost layer of metal precursor is converted to the corresponding oxide using an oxygen containing reactant, such as water or ozone, thus removing impurities from the high-k/noble metal interface.